STcorr: An IDL code for image based normalization of lapse rate and illumination effects on nighttime TIR imagery

Thermal infrared imagery (TIR) is a useful tool to detect and quantify the surface temperature anomalies associated with geothermal fields. Accurate detection of anomalies in surface temperature is an important aspect of geothermal research. Although day-time TIR images have long been used for temperature anomaly mapping, the increase in the spatial resolution and the number of acquisitions of nighttime thermal imagery provide new perspectives to the remote geothermal monitoring and exploration. However, the nighttime thermal imagery requires appropriate corrections in order to minimize some major artefacts. These corrections are namely: the masking of small scale thermal anomalies by the lapse rate, the relict diurnal heat due to the radiation of sun and the slope effect. Moreover, the correction of nighttime TIR imagery according to the altitude, slope aspect and the slope of the study area provide more reliable data. STcorr is an Interactive Data Language (IDL) code for the correction of altitude, aspect and slope effects in nighttime thermal imagery using image based polynomial regression analysis. Standard ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) Surface Kinetic Temperature (ST) image and Digital Elevation Model (DEM) are used to calculate a lapse rate model. Upon the retrieval of lapse rate, an illumination correction is performed based on the relationship between the corrected image and the aspect and slope images, interactive and “step by step” structure of the code permit user to improve the quality of the output. An ASTER nighttime ST image of the Mt. Nemrut volcano has been corrected using STcorr as an example. The procedure improves the reliability of the output after the retrieval of altitude, aspect and slope effects. Thermal anomalies observed in the Mt. Nemrut are consistent with the hydrothermal activity and the hot spots detected by self-potential measurements in the area.